1. Field of the Invention
This invention relates to a gas-turbine engine control system, particularly to a system for controlling stationary gas-turbine engines.
2. Description of the Related Art
Recent years have seen advances in the development of small gas-turbine engines, particularly stationary gas-turbine engines, that are used in combination with relatively small output generators to build independent power plants. Gas-turbine engines of this type use a gaseous fuel that is mixed with air and supplied to a combustion chamber (combustor) to produce premixed combustion or diffusive combustion.
Emission performance, while differing with combustion mode, is characterized by increasing NOx emission concentration with rising combustion temperature. Still, premixed combustion, which can achieve combustion with a homogenous or uniform temperature distribution, is superior to premixed combustion in the point of low emission operation. However, premixed combustion is possible only within a limited range because its low combustion temperature in comparison with diffusive combustion makes the combustion unstable and susceptible to flameout.
On the other hand, diffusive combustion is possible over the entire combustion range but the presence of scattered high-temperature sites increases NOx emission concentration. In order to achieve low emission operation, therefore, it is preferable to switch the combustion mode from diffusive combustion to premixed combustion whenever premixed combustion is possible.
For this purpose, Japanese Laid-open Patent Application No. 2000-248964 (corresponding to U.S. Pat. No. 6,282,885) teaches switching of combustion (combustion mode) in a gas-turbine engine in response to load state or turbine rpm.
Combustion state is, however, difficult to estimate from load state or turbine rpm. Switching of the combustion mode based on these factors therefore does readily enable effective utilization of premixed combustion within the narrow combustion range of this mode.
An object of this invention is therefore to overcome the foregoing problem by providing a system for controlling a gas-turbine engine that mixes air and gaseous fuel in venturi mixers in accordance with whichever combustion mode between premixed combustion and diffusive combustion has been selected and supplies the resulting air-fuel mixture to a combustor to rotate the turbine, which determines the adiabatic flame temperature and the venturi mixer inlet temperature, and switches the combustion mode based on these temperatures, thereby achieving switchover to the stabler combustion mode and realizing better low emission performance by utilizing the premixed combustion range.
Moreover, when the flow rate of air supplied to the venturi mixers is used when determining the adiabatic flame temperature, the flow rate is preferably determined with high accuracy.
Another object of this invention is therefore to provide a system for controlling a gas-turbine engine control system that mixes air and gaseous fuel in venturi mixers in accordance with whichever combustion mode between premixed combustion and diffusive combustion has been selected and supplies the resulting air-fuel mixture to a combustor to rotate the turbine, which determines the air flow rate with high accuracy, determines the adiabatic flame temperature with high accuracy using the air flow rate, and switches the combustion mode based on the adiabatic flame temperature etc.
The present invention achieves the foregoing objects by providing a system for controlling a gas-turbine engine having a plurality of venturi mixers, connected to an air supply path that passes air compressed by a compressor and to a supply source of gaseous fuel, which mix the air and the fuel in response to selected one of combustion modes comprising premixed combustion and diffusive combustion, to produce an air-fuel mixture and supply the air-fuel mixture to a combustion chamber such that produced combustion gas rotates a turbine that outputs its rotation through an output shaft, while driving the compressor by the rotation; comprising: detecting means for detecting a temperature of the air supplied to the mixers and a pressure of the fuel supplied to the mixers; flow rate determining means for determining a flow rate of the fuel supplied to the mixers based on at least the detected pressure of the fuel; adiabatic flame temperature determining means for determining an adiabatic flame temperature in the combustion chamber based on at least the determined flow rate of the fuel; combustion switching determination conducting means for conducting a determination as to whether the selected one of the combustion modes is to be switched to other of the combustion modes, based on the determined adiabatic flame temperature and the detected air temperature; and combustion switching controlling means for controlling to switch the selected one of the combustion modes to the other in response to a result of determination of the combustion switching determining means.